Preheat the oven to 350°F and line an 8×8-inch metal pan with parchment paper.
In a large bowl, stir together the melted butter, flour, oats, sugar, cinnamon and salt. The mixture will be dry and sandy with some larger, well-formed crumble pieces. This makes up the crust and crumble. Set 1 heaping cup (I used almost 1 1/2 cups) of the mixture aside for the crumb topping.
1 cup unsalted butter, 2 cups all-purpose flour, 1 1/2 cups old-fashioned rolled oats, 1 teaspoon cinnamon, 1/2 teaspoon salt, 1 cup light brown sugar
Transfer the remaining crumb mixture to the prepared pan, and use a spatula or your fingers to press the mixture evenly into the bottom of the pan to create an even crust,
Spread the cranberry sauce evenly over the crust. Sprinkle the reserved crumb topping over the cranberry sauce. There will be cranberries still showing, this is what you want.
1 can whole cranberry sauce
Bake in the preheated oven for 50-55 minutes, or until the crumble is golden and the blueberrries are bubbling around the edges. Check the bars with 15 minutes remaining and cover with foil if the top is starting to look to brown.
Allow the bars to cool for 1 hour then use the parchment paper overhang to remove the bars and cool them completely. You can place them in the freezer to speed up the cooling process. Slice cooled bars into squares and enjoy with ice cream